CN111703413B - Lateral control safety monitoring method and system for automatic driving vehicle - Google Patents

Lateral control safety monitoring method and system for automatic driving vehicle Download PDF

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CN111703413B
CN111703413B CN201910204708.1A CN201910204708A CN111703413B CN 111703413 B CN111703413 B CN 111703413B CN 201910204708 A CN201910204708 A CN 201910204708A CN 111703413 B CN111703413 B CN 111703413B
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vehicle
lateral
steering wheel
angle
transfer rate
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CN111703413A (en
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鲁宁
张凯
和林
甄龙豹
葛建勇
王天培
张健
贾卓
张露
高莎莎
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Haomo Zhixing Technology Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
    • B60W10/20—Conjoint control of vehicle sub-units of different type or different function including control of steering systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
    • B60W30/02—Control of vehicle driving stability
    • B60W30/04—Control of vehicle driving stability related to roll-over prevention
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
    • B60W40/10—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to vehicle motion
    • B60W40/109—Lateral acceleration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W50/0098—Details of control systems ensuring comfort, safety or stability not otherwise provided for
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W2050/0001—Details of the control system
    • B60W2050/0043—Signal treatments, identification of variables or parameters, parameter estimation or state estimation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/12—Lateral speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2710/00—Output or target parameters relating to a particular sub-units
    • B60W2710/20—Steering systems

Abstract

The invention relates to the technical field of intelligent traffic, and provides a transverse control safety monitoring method and system for an automatic driving vehicle. The method comprises the following steps: establishing rollover stability evaluation indexes of the vehicle, including a transverse load transfer rate; determining factors influencing the transverse load transfer rate, including lateral acceleration, and taking the lateral acceleration as a stability control target corresponding to the transverse load transfer rate; establishing a corresponding relation between lateral acceleration and longitudinal speed, a front wheel corner and vehicle parameters according to a vehicle dynamic model and the vehicle parameters; acquiring the maximum steering wheel corner corresponding to the maximum lateral acceleration at different speeds as a corner threshold according to the corresponding relation and the conversion relation between the front wheel corner and the steering wheel corner; and limiting the steering wheel angle to a steering angle threshold when the steering wheel angle is greater than the steering angle threshold. Compared with the traditional scheme of directly providing the extreme limit value, the method is more suitable for different working conditions and continuously changing vehicle states.

Description

Transverse control safety monitoring method and system for automatic driving vehicle
Technical Field
The invention relates to the technical field of intelligent traffic, in particular to a transverse control safety monitoring method and system for an automatic driving vehicle.
Background
The design and development of an autonomous driving (also called unmanned, intelligent driving) system can be roughly divided into four modules: environmental perception, data fusion, decision planning and motion control. To realize automatic driving, an automatic driving vehicle needs to fully understand surrounding environment like human, including all environmental information affecting driving behaviors, such as surrounding vehicles, pedestrians, road signs, road surfaces, weather and the like, namely environment perception. And secondly, processing all the acquired sensor information by the automatic driving system, including extraction, screening, filtering, comparison and the like, and finally obtaining stable signals which can truly reflect the information of the surrounding environment of the vehicle, namely data fusion. And then, the automatic driving system makes corresponding judgment and planning according to the fused information, and the judgment and planning comprise the steps of keeping the contents of current road driving, lane changing, driving tracks, driving speed and the like, namely decision planning. And finally, controlling the vehicle to complete corresponding actions by the automatic driving system according to the received decision-making instruction, wherein the actions comprise keeping running in the current lane, changing lanes, running at a specified speed, following the previous vehicle, and the like, namely motion control.
The motion control module is used as a bottom module of the automatic driving control system, and is very easily influenced when other modules are in error operation. For example, a sudden failure or signal abnormality of a certain sensor causes an input abnormality of the automatic driving system, thereby causing erroneous calculation, and finally resulting in an erroneous output. This erroneous output may cause the vehicle to suddenly turn or suddenly brake and accelerate, which may cause the passenger to feel uncomfortable at a light rate and cause the vehicle to sideslip and roll over at a heavy rate, thus seriously defeating the purpose of the automatic driving system.
Therefore, in order to ensure the safety of the control of the automatic driving system, a safety monitoring function needs to be added to a motion control module of the automatic driving system so as to realize the safety monitoring of the transverse and longitudinal control quantity. According to the output of the motion control module, the related safety monitoring function comprises two parts: one part is used for carrying out safety monitoring on longitudinal control, and the other part is used for carrying out safety monitoring on transverse control. The aim of safety monitoring for transverse control is mainly to ensure that the moving vehicle does not have the risks of side turning, sideslip and the like.
However, current lateral control safety monitoring schemes directly limit the amount of control output to an extreme value (e.g., u)min≤u≤umaxWhere u is the output value, uminIs the upper limit of output, umaxLower output limit). Although the scheme can achieve a certain monitoring purpose, the method is too general and simple and cannot adapt to different working conditions and continuously-changed vehicle states. The end result is often: the effect of safety monitoring cannot be achieved under some working conditions; and the control function of the control system is restricted under other working conditions. Therefore, new lateral control safety monitoring strategies need to be designed to improve safe driving of autonomous vehicles.
Disclosure of Invention
In view of the above, the present invention is directed to a lateral control safety monitoring method for an autonomous vehicle, so as to at least partially solve the above technical problems.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a lateral control safety monitoring method for an autonomous vehicle, comprising: establishing a rollover stability evaluation index of the vehicle, wherein the rollover stability evaluation index comprises a transverse load transfer rate of the vehicle; determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle, wherein the factor influencing the transverse load transfer rate is determined and comprises the lateral acceleration of the vehicle, and the lateral acceleration is used as the stability control target corresponding to the transverse load transfer rate; establishing a corresponding relation between the lateral acceleration and the longitudinal speed, between a front wheel corner and between the front wheel corner and the vehicle parameters according to a vehicle dynamic model and the vehicle parameters; acquiring the maximum steering wheel angle corresponding to the given maximum lateral acceleration under different vehicle speeds according to the corresponding relation and the conversion relation between the front wheel angle and the steering wheel angle of the vehicle, and taking the maximum steering wheel angle as a steering angle threshold value; and monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.
Further, the rollover stability evaluation index further includes one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.
Further, the determining a factor that affects the lateral load transfer rate includes:
first, a mathematical model expressing the lateral load transfer rate is established as follows:
Figure BDA0001998603510000031
wherein LTR represents the lateral load transfer rate, ayRepresenting the lateral acceleration, h representing the height of the centre of mass, hsThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;
secondly, determining factors that affect the lateral load transfer rate includes any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.
Further, the corresponding relationship between the lateral acceleration and the longitudinal speed, the front wheel rotation angle and the vehicle parameters is as follows:
Figure BDA0001998603510000032
wherein, ayIs said lateral acceleration, k1Is front axle equivalent yaw stiffness, k2For rear axle equivalent yaw stiffness, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, and u is the longitudinal vehicle speedAnd δ is a front wheel turning angle.
Further, the conversion relationship between the front wheel rotation angle and the steering wheel rotation angle of the vehicle is as follows:
δsw＝δi
where δ is the front wheel angle, δswAnd i is the steering wheel angle, and i is the steering system transmission ratio.
Compared with the prior art, the transverse control safety monitoring method based on vehicle dynamics design can achieve the purpose of safety monitoring, especially can ensure the safe driving of the vehicle under the high-speed working condition, and further improves the safety of an automatic driving system, so that the transverse control safety monitoring method is more suitable for different working conditions and continuously changing vehicle states compared with the traditional scheme of directly providing an extreme value limiting value.
Another object of the present invention is to propose a machine readable storage medium to at least partially solve the above technical problem.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a machine-readable storage medium having instructions stored thereon for causing a machine to perform the lateral control safety monitoring method for an autonomous vehicle described above.
The machine-readable storage medium has the same advantages as the above-mentioned lateral control safety monitoring method over the prior art, and is not described herein again.
Another object of the present invention is to propose a lateral control safety monitoring system of an autonomous vehicle to at least partially solve the above technical problem.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a lateral control safety monitoring system for an autonomous vehicle, comprising: the index establishing module is used for establishing a rollover stability evaluation index of the vehicle, and the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle; the target determination module is used for determining factors influencing the rollover stability evaluation index as a stability control target of the vehicle, and determining factors influencing the transverse load transfer rate, wherein the factors comprise the lateral acceleration of the vehicle, and the lateral acceleration is used as the stability control target corresponding to the transverse load transfer rate; the relation establishing module is used for establishing the corresponding relation between the lateral acceleration and the longitudinal speed, the corner of the front wheel and the vehicle parameters according to a vehicle dynamic model and the vehicle parameters; a threshold value determining module, configured to obtain a maximum steering wheel angle corresponding to the given maximum lateral acceleration at different vehicle speeds according to the correspondence and a conversion relationship between the front wheel angle and a steering wheel angle of the vehicle, and use the maximum steering wheel angle as a steering angle threshold value; and the monitoring module is used for monitoring the steering wheel angle in real time and judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, the steering wheel angle is limited to the steering wheel threshold value and then output for vehicle transverse control, otherwise, the steering wheel angle is normally output for vehicle transverse control.
Further, the rollover stability evaluation index further includes one or more of a roll angle threshold, a lateral acceleration threshold, and a rollover time.
Further, the determining a factor that affects the lateral load transfer rate includes:
first, a mathematical model expressing the lateral load transfer rate is established as follows:
Figure BDA0001998603510000051
wherein LTR represents the lateral load transfer rate, ayRepresenting the lateral acceleration, h representing the height of the centre of mass, hsThe distance from the center of mass to the center of rollover is shown, g is the gravity acceleration, phi is the vehicle roll angle, and B is the vehicle wheel track;
secondly, determining factors that affect the lateral load transfer rate includes any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.
Further, the corresponding relationship between the lateral acceleration and the longitudinal vehicle speed and the steering wheel angle is as follows:
Figure BDA0001998603510000052
wherein, ayIs said lateral acceleration, k1Is front axle equivalent yaw stiffness, k2And (3) equivalent cornering stiffness of the rear axle, wherein a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, u is the longitudinal speed, and delta is the corner of the front wheel.
Compared with the prior art, the transverse control safety monitoring system and the transverse control safety monitoring method have the same advantages, and are not described again.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation of the invention. In the drawings:
FIG. 1 is a schematic flow diagram of a lateral control safety monitoring method for an autonomous vehicle in accordance with an embodiment of the invention;
FIG. 2 is a schematic diagram of a physical model of lateral load transfer rate for an embodiment of the present invention;
FIG. 3 is a graph of maximum steering wheel angle at different vehicle speeds in an actual measurement example of an embodiment of the present invention; and
fig. 4 is a schematic structural diagram of a lateral control safety monitoring system of an autonomous vehicle according to an embodiment of the present invention.
Description of reference numerals:
410. index establishing module 420 and target determining module
430. Relationship establishing module 440 and threshold determining module
450. Monitoring module
Detailed Description
In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.
The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Fig. 1 is a schematic flow chart of a lateral control safety monitoring method for an autonomous vehicle according to an embodiment of the present invention. As shown in fig. 1, the self-lateral control safety monitoring method may include the steps of:
and step S110, establishing rollover stability evaluation indexes of the vehicle.
Rollover is an important index of vehicle stability, and is also a control index which needs to pay attention to in the transverse control of the automatic driving vehicle. Rollover stability has a history of more than 20 years, but casualties and economic losses caused by rollover are the most serious. Therefore, the rollover stability evaluation index is determined in the transverse control safety monitoring, and the introduction of the vehicle rollover control potential is considered to be imperative.
When the rollover of the vehicle is researched, firstly, an evaluation index for measuring the rollover risk degree of the vehicle needs to be provided, and the index also needs to judge whether the vehicle reaches a critical rollover point. First, rollover refers to a dangerous situation in which a vehicle turns over more than a large right angle around its driving direction as an axis during movement, resulting in collision of the vehicle body with the ground. Under actual conditions, particularly for vehicle rollover caused by curvilinear motion, due to the fact that high-speed moving vehicles have large inertia, rollover accidents of the vehicles occur in most cases when one side wheel is away from the ground. Only a few drivers driving a particular vehicle can keep running and return to a steady state at the moment when the wheels lift off the ground. Therefore, the evaluation index of the rollover stability is different for different situations.
Since the vertical load of the wheels on one side is basically 0 when the vehicle moves at high speed, rollover accidents can happen, and therefore the vertical load of each wheel of the vehicle in high-speed movement needs to be measured in real time when the vehicle is researched to rollover. However, it is difficult to measure the load on the wheels when the vehicle is moving, so parameters need to be converted, and the conversion process is to convert the whole vehicle mechanical conditions of the single-side wheels from the ground. The evaluation indexes finally used are different according to different condition changes.
Based on this, the rollover stability evaluation index in the embodiment of the present invention includes one or more of a roll angle threshold, a Lateral acceleration threshold, a rollover time, and a Lateral-Load Transfer Rate (LTR). The roll angle threshold and the lateral acceleration threshold can be used for describing the rollover state of the vehicle, and the two indexes can be obtained through static tests. Specifically, the roll angle and lateral acceleration at different phases can be measured or calculated while the vehicle is in motion, compared to a threshold, and if closer to equal or exceed the threshold, the rollover will be more likely to occur. The biggest problem of the two evaluation indexes is that static tests of different vehicle types are required to obtain closed values of corresponding parameters of the vehicle types.
The lateral load transfer rate is a commonly used index for expressing the vertical load change condition of the wheel, and in the embodiment of the invention, the lateral load transfer rate can also be used for evaluating the rollover stability of the whole vehicle. The lateral load transfer rate is the ratio of the difference and the sum of vertical loads of the left wheel and the right wheel of the vehicle, and the expression is as follows:
Figure BDA0001998603510000071
wherein LTR represents the lateral load transfer ratio, and FzlAnd FzrRespectively, represents vertical loads acting on left and right wheels, and satisfies the following equation:
Fzl+Fzr＝mg (2)
in the formula (2), m is the total mass of the vehicle, and g is the gravitational acceleration. Considering the driving condition of the vehicle, when the vehicle turns, the vertical load of the wheel inside the curve is reduced and the vertical load of the wheel outside the curve is increased correspondingly. From the definition of rollover, it is clear that:
Figure BDA0001998603510000081
the magnitude of the lateral load transfer rate is irrelevant to vehicle types, vehicle body parameters and the like, and the absolute value is about 1, so that the lateral load transfer rate is easy to compare, therefore, the lateral load transfer rate is suitable for all types of vehicles (including automatic driving vehicles), and has certain universality for researching vehicle types which are easy to roll over, such as SUVs, semi-trailer trains and the like.
In specific practice, based on the above equations (1) to (3), Simulink simulation software can be used to establish an anti-rollover model of the vehicle, so that the simulation process can measure some vehicle operation parameters which are difficult to obtain in real time, such as roll angle, LTR and other parameters. LTR can evaluate the rollover prevention performance of the vehicle from different aspects, so that the embodiment of the invention adopts the LTR parameter as a rollover stability evaluation index, and the following steps are taken as examples.
And step S120, determining a factor influencing the rollover stability evaluation index as a stability control target of the vehicle.
Taking the lateral load transfer rate as an example, the step S120 specifically includes: determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and taking the lateral acceleration as the stability control target corresponding to the lateral load transfer rate.
More specifically, a mathematical model is first established, which can express the influence of the lateral load transfer rate LTR on what parameters, and the physical model is shown in fig. 2. Based on a physical model, in the construction of a data model, the road surface is assumed to be flat, the roll of the mass of an axle is ignored, and the wheel tracks of front and rear axles are assumed to be the same, namely Br＝Bl. Suppose that the sprung mass is msH is the height of the center of mass, hsIs the distance from the center of mass to the center of rollover, g is the gravitational acceleration, phi is the equivalent roll angle,
Figure BDA0001998603510000094
in order to be equivalent to the roll stiffness,
Figure BDA0001998603510000095
for equivalent roll damping, the vehicle is controlledTaking the moment balance equation for the ground reaction point of the vehicle's side-tipping inboard wheel (the inboard wheel is the right wheel in fig. 2), one can obtain:
Figure BDA0001998603510000091
by the same method, the moment of the vehicle roll outer side wheel is obtained, and the following can be obtained:
Figure BDA0001998603510000092
because phi is smaller, sin phi is taken as phi; when taking LTR value, the model ignores unsprung mass, i.e. m is takensM. From formulae (1), (2), (4), and (5), it is possible to obtain:
Figure BDA0001998603510000093
from the formula (6), the lateral load transfer rate of the vehicle rollover can be influenced by the vehicle structural parameters and the driving parameters, and the rollover state of the vehicle can be controlled by effectively controlling the parameters. According to equation (6), to lower the value of LTR, there may be the following method:
1) lowering the vehicle centroid height h, thereby also enabling hsDecreasing;
2) increasing the vehicle wheel track B;
3) reducing the vehicle roll angle Φ; and
4) reducing the lateral acceleration a of the vehicley。
These are four approaches that are the subject of rollover research. Since the structural parameters of a vehicle model are already determined in the vehicle design stage, the structural parameters such as the centroid height and the wheel track of the vehicle in the methods 1) and 2) are not changed after the vehicle is produced. Therefore, the rollover prevention control effect which can be achieved by the two methods is determined in the vehicle design stage, and the technology for controlling rollover by optimizing the structural parameters belongs to the passive rollover prevention technology. Lateral acceleration of the magnitude of the roll angle phiIn certain cases, the degree of the sprung mass roll is mainly determined by coefficients and parameters that determine the degree of the sprung mass roll, such as a suspension system of the vehicle, and therefore, it is necessary to consider the influence of the suspension in order to reduce the equivalent roll angle. It is obvious that the main reason for the rollover is due to ayThe limit is exceeded, and the vertical load of the wheel at the inner side of the curve is reduced to 0. Lateral acceleration a of vehicleyThe lateral force is generated, and the control on the lateral force usually adopts active control technology, such as active steering, differential braking and the like, so that the control on the lateral acceleration of the vehicle during turning is usually realized by adopting one or more control modes.
Therefore, to lower the value of LTR, it is necessary to consider the influence of the suspension and to select an active control technique for controlling the lateral force. Method 3) is also not considered by embodiments of the present invention, since the type of suspension is also basically determined when the vehicle is designed. Thus, embodiments of the present invention address the important issue of rollover prevention in reducing the lateral acceleration of a vehicle turning.
Step S130, establishing a corresponding relation between the lateral acceleration and the longitudinal speed, the corner of the front wheel and the vehicle parameters according to a vehicle dynamic model and the vehicle parameters.
In other embodiments, the vehicle kinematics model may also be considered to establish the corresponding relationship, but the vehicle kinematics model does not consider the stress condition in the vehicle motion process and the dynamic parameters of the vehicle itself, so that a safe control quantity cannot be obtained according to the dynamic state of the vehicle itself, and especially, the constraint that only the lateral control quantity is obtained from the kinematic point of view under some limit conditions is unreasonable. Therefore, the embodiment of the invention starts from the vehicle dynamics perspective and considers the restriction of the transverse control quantity under certain limit working conditions. The following provides a specific process for establishing the corresponding relationship between the lateral acceleration and the longitudinal speed, the front wheel rotation angle and the vehicle parameters according to a vehicle dynamic model and the vehicle parameters.
Firstly, the basic characteristics of vehicle motion can be effectively mastered by simplifying the vehicle into a linear two-degree-of-freedom bicycle model for research. According to the established two-degree-of-freedom model:
Figure BDA0001998603510000101
Figure BDA0001998603510000102
wherein, ayIs said lateral acceleration, k1Is front axle equivalent yaw stiffness, k2For equivalent yaw stiffness of the rear axle, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, m is the vehicle mass, IZIs the moment of inertia, u is the longitudinal vehicle speed, v is the lateral vehicle speed, wrThe yaw rate is shown, and δ is the front wheel angle.
It should be noted that the lateral vehicle speed v is generally small, and in the embodiment of the present invention, the influence on the steering angle is also small, so that only the longitudinal vehicle speed may be used in some cases.
Secondly, according to the optimal preview theory, assuming that the vehicle always stably runs along a curve on the road, the following error is zero, and the vehicle is in the steady state condition
Figure BDA0001998603510000111
According to formula (7):
Figure BDA0001998603510000112
from equations (7) to (8), the correspondence between the lateral acceleration and the longitudinal vehicle speed, the front wheel steering angle, and the vehicle parameter can be obtained:
Figure BDA0001998603510000113
that is, the lateral acceleration of the vehicle under steady state conditions may be expressed as a function of vehicle longitudinal speed, front wheel steering angle, and vehicle parameters.
Step S140, obtaining the maximum steering wheel angle corresponding to the given maximum lateral acceleration under different vehicle speeds according to the corresponding relation and the conversion relation between the front wheel angle and the steering wheel angle of the vehicle, and taking the maximum steering wheel angle as a steering angle threshold value.
As can be seen from equation (10), in order to reduce the lateral acceleration of the vehicle during driving, there are two ways: the longitudinal speed is reduced, and the front wheel turning angle is reduced. For the lateral safety monitoring part, the steering wheel angle needs to be restrained in order to ensure the safety of the vehicle under the condition that the longitudinal vehicle speed is constant. Therefore, the embodiment of the present invention further implements the constraint of the steering wheel angle by using the conversion relationship between the front wheel steering angle and the steering wheel angle of the vehicle.
Specifically, the conversion relationship between the front wheel steering angle and the steering wheel steering angle of the vehicle is as follows:
δsw＝δi (11)
wherein, deltaswAnd i is the steering wheel angle, and i is the steering system transmission ratio.
Further, according to the equations (10) and (11), the maximum vehicle lateral acceleration a is given at different vehicle speedsymaxThen, the maximum steering wheel angle δ can be obtainedswmaxThe calculation formula is as follows:
Figure BDA0001998603510000114
the maximum steering wheel angle deltaswmaxIs the corner threshold.
And S150, monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.
Specifically, the automatic driving system can utilize an Electric Power Steering (EPS) system to perform lateral control, so that the purpose of acquisition is achieved in an environment sensing module, a data fusion module or a decision planning moduleAfter marking the steering wheel angle, use the steering angle threshold δ before sending to the EPSswmaxLimiting, and when the calculated target steering wheel angle is larger than the steering angle threshold value at a certain moment, making the target steering wheel angle equal to the steering angle threshold value deltaswmaxOtherwise, outputting normally.
With respect to the above steps S110 to S150, the actual measurement results of the lateral control safety monitoring method according to the embodiment of the present invention are described by way of example. In this example, according to a certain type of vehicle model setting parameter, the curve of the maximum steering wheel angle at different vehicle speeds is obtained as shown in fig. 3, and it is known that the larger the vehicle speed is, the smaller the corresponding maximum steering wheel angle is, so that rollover caused by an excessively large vehicle speed can be avoided.
The actual measurement result shown in fig. 3 shows that the lateral control safety monitoring method based on vehicle dynamics design can achieve the purpose of safety monitoring, especially can ensure the safe driving of the vehicle under the high-speed working condition, and further improves the safety of the automatic driving system.
Fig. 4 is a schematic structural diagram of a lateral control safety monitoring system of an autonomous vehicle according to an embodiment of the present invention. As shown in fig. 4, the lateral control safety monitoring system may include: the index establishing module 410 is configured to establish a rollover stability evaluation index of the vehicle, where the rollover stability evaluation index includes a lateral load transfer rate of the vehicle; a target determining module 420, configured to determine a factor affecting the rollover stability evaluation indicator as a stability control target of the vehicle, including determining a factor affecting the lateral load transfer rate, where the factor includes a lateral acceleration of the vehicle, and use the lateral acceleration as the stability control target corresponding to the lateral load transfer rate; the relationship establishing module 430 is configured to establish a corresponding relationship between the lateral acceleration and a longitudinal vehicle speed, a front wheel corner and the vehicle parameter according to a vehicle dynamics model and the vehicle parameter; a threshold determining module 440, configured to obtain a maximum steering wheel angle corresponding to the given maximum lateral acceleration at different vehicle speeds according to the correspondence and a conversion relationship between the front wheel angle and a steering wheel angle of the vehicle, and use the maximum steering wheel angle as a steering wheel threshold; and a monitoring module 450, configured to monitor the steering wheel angle in real time, and determine whether the monitored steering wheel angle is greater than the steering angle threshold, if so, limit the steering wheel angle to the steering angle threshold, and then output the steering wheel angle for vehicle lateral control, otherwise, normally output the steering wheel angle for vehicle lateral control.
For details and effects of other implementation details and effects of the lateral control safety monitoring system for an autonomous vehicle according to the embodiment of the present invention, reference may be made to the above-mentioned embodiment of the lateral control safety monitoring method for an autonomous vehicle, and details are not repeated here.
In the embodiment of the invention, the transverse control safety monitoring method and the transverse control safety monitoring system can be configured in a motion control module of an automatic driving system so as to monitor the stability of transverse control of a vehicle. Compared with the conventional vehicle which can predict rollover depending on the experience of a driver, the automatic driving vehicle has higher requirement on control precision due to rollover control depending on the motion control module, and needs a perfect safety monitoring scheme.
Another embodiment of the present invention also provides a machine-readable storage medium having instructions stored thereon for causing a machine to perform the above-described lateral control safety monitoring method for an autonomous vehicle. The machine-readable storage medium includes, but is not limited to, Phase Change Random Access Memory (PRAM, also known as RCM/PCRAM), Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM), Flash Memory (Flash Memory) or other Memory technologies, compact disc read only Memory (CD-ROM), Digital Versatile Disc (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, and various other media capable of storing program code.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (6)

1. A lateral control safety monitoring method for an autonomous vehicle, the lateral control safety monitoring method comprising:
establishing a rollover stability evaluation index of the vehicle, wherein the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle;
determining a factor affecting the rollover stability evaluation index as a stability control target for the vehicle, wherein determining the factor affecting the rollover stability evaluation index as the stability control target for the vehicle comprises: determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and taking the lateral acceleration as the stability control target corresponding to the lateral load transfer rate;
according to a vehicle dynamic model and vehicle parameters, establishing corresponding relations among the lateral acceleration, the longitudinal speed, the front wheel corners and the vehicle parameters, wherein the corresponding relations among the lateral acceleration, the longitudinal speed, the front wheel corners and the vehicle parameters are as follows:
Figure FDA0003680852420000011
wherein, ayIs said lateral acceleration, k1Is front axle equivalent yaw stiffness, k2The equivalent lateral deflection stiffness of the rear axle is shown as a, the distance from the center of mass to the front axle is shown as b, the distance from the center of mass to the rear axle is shown as u, the longitudinal speed is shown as delta, the rotation angle of the front wheel is shown as delta, and the mass of the whole vehicle is shown as m;
acquiring the maximum steering wheel angle corresponding to the given maximum lateral acceleration under different vehicle speeds according to the corresponding relation and the conversion relation between the front wheel angle and the steering wheel angle of the vehicle, and taking the maximum steering wheel angle as a steering angle threshold value; and
and monitoring the steering wheel angle in real time, judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, limiting the steering wheel angle to the steering wheel threshold value and then outputting the steering wheel angle for vehicle transverse control, otherwise, normally outputting the steering wheel angle for vehicle transverse control.
2. The lateral-control safety-monitoring method of an autonomous vehicle of claim 1, wherein the determining a factor that affects the lateral load transfer rate comprises:
establishing a mathematical model expressing the transverse load transfer rate as follows:
Figure FDA0003680852420000021
wherein LTR represents the lateral load transfer rate, ayRepresents the lateral acceleration, h represents the height of the center of mass, hsThe distance from the center of mass to the center of rollover, g is the gravitational acceleration,
Figure FDA0003680852420000022
the vehicle side inclination angle is shown, and the B is the vehicle wheel track;
determining factors that affect the lateral load transfer rate includes any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.
3. The lateral-control safety-monitoring method of an autonomous vehicle of claim 1, characterized in that the conversion relationship between the front-wheel turning angle and the steering-wheel turning angle of the vehicle is:
δsw＝δi
where δ is the front wheel angle, δswAnd i is the steering wheel angle, and i is the steering system transmission ratio.
4. A machine-readable storage medium having instructions stored thereon for causing a machine to perform the lateral control safety monitoring method of an autonomous vehicle of any of claims 1 to 3.
5. A lateral-control safety-monitoring system for an autonomous vehicle, the lateral-control safety-monitoring system comprising:
the index establishing module is used for establishing a rollover stability evaluation index of the vehicle, and the rollover stability evaluation index comprises the transverse load transfer rate of the vehicle;
a target determination module configured to determine a factor that affects the rollover stability evaluation index as a stability control target of the vehicle, wherein determining the factor that affects the rollover stability evaluation index as the stability control target of the vehicle includes: determining a factor that affects the lateral load transfer rate, the factor comprising a lateral acceleration of the vehicle; and taking the lateral acceleration as the stability control target corresponding to the lateral load transfer rate;
the relationship establishing module is used for establishing corresponding relationships among the lateral acceleration, the longitudinal speed, the front wheel corners and the vehicle parameters according to a vehicle dynamic model and the vehicle parameters, wherein the corresponding relationships among the lateral acceleration, the longitudinal speed, the front wheel corners and the vehicle parameters are as follows:
Figure FDA0003680852420000031
wherein, ayIs said lateral acceleration, k1Is front axle equivalent yaw stiffness, k2Is equivalent lateral deflection rigidity of the rear axle, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, and u is the longitudinal and transverse directionsIn the direction of the vehicle speed, delta is a front wheel corner, and m is the mass of the whole vehicle;
a threshold determination module, configured to obtain a maximum steering wheel angle corresponding to the given maximum lateral acceleration at different vehicle speeds according to the correspondence and a conversion relationship between the front wheel angle and a steering wheel angle of the vehicle, and use the maximum steering wheel angle as a steering angle threshold; and
and the monitoring module is used for monitoring the steering wheel angle in real time and judging whether the monitored steering wheel angle is larger than the steering wheel threshold value, if so, the steering wheel angle is limited to be output after the steering wheel angle threshold value for vehicle transverse control, otherwise, the steering wheel angle is normally output for vehicle transverse control.
6. The lateral-control safety-monitoring system of an autonomous vehicle of claim 5, wherein the determining a factor that affects the lateral load transfer rate comprises:
establishing a mathematical model expressing the transverse load transfer rate as follows:
Figure FDA0003680852420000032
wherein LTR represents the lateral load transfer rate, ayRepresenting the lateral acceleration, h representing the height of the centre of mass, hsThe distance from the center of mass to the center of rollover, g is the acceleration of gravity,
Figure FDA0003680852420000033
is the vehicle side inclination angle, B is the vehicle wheel track;
determining factors that affect the lateral load transfer rate include any one or more of the height of center of mass, the vehicle track, the vehicle roll angle, and the lateral acceleration.
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